Assessment of essential and non-essential metals in popcorn and cornflake commercially available in Ethiopia

Abstract

The levels of essential and non-essential metals in popcorn and cornflake were determined in samples collected from an open market and supermarkets in Addis Ababa, Ethiopia. The samples were mineralized by wet digestion method. The volumes of reagents, digestion temperature and digestion time were optimized after proper sample pretreatment. 1 g of the powdered sample was digested with 10 mL of the mixture of HNO3 (69-72%), HClO4 (60%) and H2O2 (30%) in a volume ratio of 6:2:2 (v/v) for 3 hours at 120 0C on a Kjeldahl digestion apparatus. The levels of metals in the digest were determined by flame atomic absorption spectrometry (for major metals: K, Na, Mg, Ca) and graphite furnace atomic absorption spectrometry (for trace and heavy metals: Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb, Cd). The accuracy of the optimized procedure was evaluated by analyzing the digest of the spiked samples with standard solution and the percentage recoveries varied from 91.2–109%. The level of the metals determined (mg/kg dry weight) were: K 1293±233, Na 148±3, Mg 387±11, Ca 97.9±4.2, Cr 0.68±0.09, Mn (6.17±0.18, Fe 9.5± 2.1, Co 1.41±0.16, Cu 0.09±0.007, Zn 88.3±9.7 and Pb 0.94±0.29 in the popcorn and K 612±70, Na 410±5, Mg 323±11, Ca 196±99, Cr 0.30±0.0.07, Mn 3.0±0.1, Fe 5.5±0.74, Co 0.32±0.03, Cu 0.30±0.01, Zn 40.7±2.5 and Pb 0.36±0.03 in the cornflake while the concentration of Cd and Ni were below the detection limit in both the samples. K and Zn were present at the highest levels among major and trace metals, respectively. The popcorn and cornflake samples purchased from Addis Ababa (Ethiopia) were free from the toxic metals Cd and Ni, but not from Pb.